1. Field of the Disclosure
The present disclosure relates to a semiconductor light-emitting device, and particularly to a nitride-based semiconductor light-emitting device having an improved structure to enhance light extraction efficiency, and a method of manufacturing the same.
2. Description of the Related Art
Light-emitting diodes (LED) are devices used for emitting electrical energy in the form of infrared rays, visible light, or the other light using the characteristics of compound semiconductors. A group III nitride compound semiconductor is a direct transition semiconductor. The group III nitride compound semiconductor is widely utilized in light-emitting devices, such as, LEDs or laser diodes (LDs) because this LED or LD can more stably operate at high temperatures compared to devices which use the other semiconductors. Such a group III nitride compound semiconductor is generally formed on a substrate of sapphire(Al2O3) or SiC. The emission efficiency of the LED depends on the internal quantum efficiency and light extraction efficiency thereof. In order to improve the light-emitting efficiency, a variety of structures of light-emitting diodes that improve light extraction efficiency are under development.
FIGS. 1A and 1B are schematic views showing light paths depending on the structure of an interface between the material layers having different refractive indexes. In FIG. 1A, a first material layer 2 has a flat interface 8a and in FIG. 1B, a first material layer 2 has a rough interface 8b. 
Referring to FIG. 1A, when light seeks to pass from the first material layer 2 having a greater refractive index into an air layer 4 having a smaller refractive index (n=1), the light must enter the flat interface 8a at at least a predetermined angle. If the light enters at an angle smaller than the predetermined angle, the light is totally internally reflected at the flat interface 8a and the light extraction efficiency is largely reduced. Therefore, a method of making an interface non-flat has been attempted in order to avoid a reduction of the light extraction efficiency.
Referring to FIG. 1B, by forming the rough interface 8b between the first material layer 2 and the air layer 4, light passing from the first material layer 2 into the air layer 4 maintains an angle equal to or greater than the predetermined incidence angle at the rough interface 8b. As a result, at the rough interface 8b rather than the flat interface 8a, the light extraction efficiency is remarkably increased.
A conventional nitride-based compound semiconductor LED is manufactured by sequentially performing the operations of sequentially forming an n-clad layer, an active layer, and a p-clad layer on a substrate; forming an n-contact surface by etching from a portion of the upper surface of the p-clad layer to a desired depth of the n-clad layer; forming an n-electrode on the n-contact surface; and forming a p-electrode on the p-clad layer. Since the nitride-based compound semiconductor has a reflective index higher than that of an air layer (n=1), for example, has a GaN reflective index n of 2.54, it is difficult in a conventional LED structure for the light generated at the active layer to pass through the flat GaN surface and to be extracted outwardly. Thus the light extraction efficiency of the nitride-based semiconductor LED is not high. In order to resolve this problem, it is proposed that a rough surface is formed on the p-contact layer or the n-contact layer. Japanese Patent Publication No. 2004-221529 discloses a method of forming a rough surface at a surface of a non-electrode region where no p-type and n-type electrode layers are formed. However, in these proposed methods, the rough surface is formed by depositing a metal dot mask on the surface of the p-contact layer and wet etching the p-contact layer, or by dry etching the n-clad layer to form an n-contact layer and wet etching the surface of the n-contact layer, or by performing additional lithography and dry etching on the surface of the non-electrode region. Thus, the above-proposed methods require many additional processes. Also, in order to simultaneously obtain the three structures described above, all of the above processes must be performed, thereby complicating the manufacturing process. Further, in a conventional technique of forming a rough surface, a process for forming a semiconductor light-emitting device is performed and then an additional chemical etching process is performed. Thus, the manufacturing process is complicated and the productivity is low.